Apparatus and method for transient and uninterruptible power

ABSTRACT

In accordance with certain exemplary embodiments, the present technique provides methods and apparatus for providing transient and uninterrupted power to protected loads. As one example, the present invention provides an induction device that operates as an induction motor to energize a kinetic energy storage device, such as a flywheel, during conventional operating conditions. However, in the event of a loss of primary power, the induction device, which is fed ac power at variable frequencies, begins to operate as an induction generator. For example, by varying the frequency of the input ac power such that the synchronous speed of the motor is exceeded by the rotating flywheel, the induction device acts as an induction generator and provides a transient operating power to the downstream loads until an auxiliary power source, such as a diesel generator, is brought on line.

BACKGROUND

The present invention relates generally to a transient power supply and,more particularly, to method and apparatus for providing transient powerby converting stored kinetic energy into electrical energy.

Typically, electrical devices receive operating power from an externalpower distribution grid that is coupled to a power generation facility,such as a power plant, for example. From time to time, this externalpower source can be interrupted, because of a malfunction in thegeneration facility and/or in the distribution grid, for instance.Accordingly, certain electrical devices are connected to an auxiliarypower source, such as a diesel generator or a bank of batteries.Unfortunately, transitioning from the external power supply to theauxiliary power supply is generally not instantaneous and, as such,presents an interval of time during which the electrical devices arewithout power. For certain critical devices, such as computers ormedical devices, even a momentary loss of power can lead to undesirableeffects, such as a loss of critical data and/or malfunction of thedevice.

Accordingly, these critical devices traditionally have been coupled to atransient power supply, which is often referred to as an uninterruptiblepower supply (UPS) by those of ordinary skill of art in the industry. Insummary, a transient power supply (i.e., UPS) provides operating powerto the critical device from when the primary power is lost to the timeat which the auxiliary power is brought on-line. Traditionally, batterybanks have been employed to provide this transient power. As anotherexample, certain flywheel devices have been employed to providetransient power.

Traditional flywheel devices include a rotating flywheel that is coupledto a generator and a motor. During normal operation, the motor operatesoff of main or primary power and energizes (i.e., kinetic energy ofrotation) the flywheel. However, when power is lost, the flywheelremains in motion and operates a traditional generator, which generatespower by rotating a permanent magnet or electromagnet within a statorcore to induce current within stator windings disposed around thepermanent magnet or electromagnet.

Unfortunately, traditional transient or UPS power sources are notwithout drawbacks. For example, battery banks that provide sufficientlevels of power can be relatively expensive to purchase and maintainand, furthermore, often consume relatively large areas of floor space.In an industrial setting, for instance, cost and floor space arerelevant concerns. As another example, traditional flywheel devicesoften require the maintenance of high rotation rates to generatesufficient and appropriate power. Accordingly, traditional flywheeldevices often employ vacuum chambers to reduce the dissipation ofkinetic energy from the flywheel due to air resistance, for example.Additionally, traditional flywheel devices employ a motor to energizethe flywheel and a separate permanent magnet generator to convert thekinetic energy of the flywheel in to electrical power. By using twodistinct devices (i.e., the generator and the motor), traditionalsystems bear a greater cost, and the use of the permanent magnet alsoincreases the cost of the system. Furthermore, maintaining a vacuumcondition for the flywheel increases the cost and likelihood of failurefor the system.

Therefore, there exists a need for improved methods and apparatus forproviding a transient power supply to certain electrical devices.

BRIEF DESCRIPTION

In accordance with one exemplary embodiment, the present techniqueprovides a power supplying apparatus. The exemplary power supplyingapparatus includes a kinetic energy storage device, such as a rotatableflywheel. The exemplary power supplying apparatus also includes a rotorthat is disposed in a stator and that is mechanically coupled to thekinetic energy storage device. The exemplary stator includes statorwindings that receive power from a power source that is capable ofproviding alternating current (ac) power to the stator windings atvariable frequencies to generate power by converting the kinetic energyof the flywheel into electrical energy.

During standard operation conditions, the exemplary power supplyingapparatus functions as an induction motor, thereby energizing thekinetic energy storage device. However, if the external power supply tothe apparatus is lost, then the exemplary apparatus functions as atransient power supply to coupled loads. By way of example, theenergized flywheel (i.e., the kinetic energy device) continues to rotateeven after a loss of external power and, as such, causes the rotor,which is mechanically coupled to the flywheel, to rotate as well. Byproviding ac power to the stator windings at an appropriately selectedfrequency, the exemplary power supplying device acts as an inductiongenerator, for example. That is, the rotation of the rotor by theflywheel in conjunction with providing ac power at the appropriatefrequency causes the rotor to rotate faster than the synchronous speedof the apparatus and, as such, generates ac power. This generated acpower is, by way of example, fed to a downstream load, thereby providingtransient operating power to the downstream load during the loss ofprimary power, for instance.

In accordance with another exemplary embodiment, the present inventionprovides a method for providing transient power to a downstream load.The exemplary method includes the act of energizing a kinetic energystorage device, such as a rotatable flywheel. By way of example, theexemplary flywheel is coupled to a rotor of an electric machine, such asan induction device. In the exemplary method, providing ac power to thestator windings of the induction device induces current in the rotorand, in turn, causes the rotor to rotate. However, upon the loss ofexternal operating power, for instance, the exemplary method actuatesthe rotor via the rotational energy stored in the flywheel. Incooperation with this actuation, the exemplary method includes that actof transmitting ac power to the stator winding at a selected frequencyto generate power from the electric machine. That is, the ac power istransmitted at a frequency that causes the electric machine to operateas an induction generator and produce a transient operating power forthe downstream load, for instance.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic of a power distribution system for a protectedload, in accordance with an embodiment of the present invention;

FIG. 2 is a schematic of a power distribution system for a protectedload, in accordance with an embodiment of the present invention;

FIG. 3 is a perspective view of a transient power supply device, inaccordance with an embodiment of the present invention;

FIG. 4 is a cross-sectional view of a the transient power supply deviceof FIG. 3 along line 4—4; and

FIG. 5 is a block diagram of an exemplary process for providingtransient power, in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION

As discussed in detail below, the present invention provides methods andapparatus for providing power to loads. Although the followingdiscussion focuses on providing transient power to a load, the presentinvention affords benefits to a number of power generation scenarios.Furthermore, the following discussion merely provides exemplaryembodiments, and these examples are not intended to limit the scope ofthe appended claims. Additionally, as a preliminary matter, thedefinition of the term “or” for the purposes of the following discussionand the appended claims is intended to be an inclusive “or.” That is,the term “or” is not intended to differentiate between two mutuallyexclusive alternatives. Rather, the term “or” when employed as aconjunction between two elements is defined as including one element byitself, the other element itself, and combinations and permutations ofthe elements. For example, a discussion or recitation employing theterminology “‘A’ or ‘B’” includes: “A” by itself, “B” by itself, and anycombination thereof, such as “AB” and/or “BA.”

Turing to the figures, FIG. 1 is a diagrammatic representation of apower distribution system 10. By way of example, the exemplary powersystem 10 is representative of a power distribution system in any numberof facilities where continuous (i.e., uninterrupted) power distributionis a concern. For example, facilities such as hospitals, data centersand emergency facilities generally benefit from uninterrupted power. Theexemplary power distribution system 10 includes an external power source12, such as a power generation plant, that provides operating power to aprotected load 14 during conventional operating conditions. For example,the external power source 10 provides ac power to the protected load 14,which may be a medical device, a data storage computer or acommunications device, to name but a few examples. To manage thedistribution of operating power to the protected load, the powerdistribution system 10 includes switching/protection/distributioncircuitry 16. The switching/protection/distribution circuitry 16provides an electrical conduit for providing operating power to theprotected load 14 from various power sources, which are discussedfurther below.

Under certain conditions, the external power source 12 can be lost. Forexample, in the event of a power outage or a transmission line failure,external power from the external power source 12 is no longer availableto the protected load 14. Indeed, due to certain events, such as weatherevents, external power may be lost for relatively long durations oftime. To mitigate the effects of a loss of external power, the exemplarypower distribution system 10 includes an auxiliary power source 18, suchas a diesel generator. Advantageously, the exemplary auxiliary powersource 18 is capable of providing operating power to the protected loadfor extended periods of time. However, delays in activating theauxiliary power source 18 from the time of loss of external power leavesthe protected load 14 without operating power during this interval. Forexample, in the case of a diesel generator, a period of seconds may passbetween the time external power is lost and the time the dieselgenerator is capable of providing operating power (i.e., broughton-line). This lag time can cause the protected load to deactivate,leading to a loss of data, for instance.

To provide operating power during this transition between power sources,the exemplary power distribution system includes an uninterruptiblepower supply (UPS) power source 20. As discussed further below, the UPS20 provides transient operating power to the protected load from thetime when external power is lost to the time the auxiliary power source18 is brought on-line. Accordingly, the protected load 14 in theexemplary power distribution system 10 never realizes a loss ofoperating power. Additionally, the protected load 14, in the exemplarypower distribution system 10, receives transient power from a batterypower source 22. However, it is worth noting that the battery powersource 22 is included as an optional component in the exemplaryembodiment, and other embodiments of the present technique can beconfigured to receive all transient power from the UPS power source 20and, as such, do not include a battery power source 22.

To manage and/or monitor the various power sources as well as theprotected load, the exemplary power distribution system 10 includes amain processor/controller 24 that is in communication with the variouscomponents of the power distribution system 10. In the exemplary powerdistribution system 10, the main processor/controller includes logiccircuitry configured to automate control and monitoring the powerdistribution system 10. Advantageously, the exemplary mainprocessor/controller 24 is configured to communicate with remotelocations via a network, for example.

FIG. 2 illustrates in further detail an exemplary power distributionsystem (PDS) 10. In the exemplary PDS 10, the external power source 14provides three-phase 480 Vac power to the system, and this power isdistributed throughout the system over an ac bus 26. The exemplary acbus 26 includes three conductive pathways 28, each of which carries onephase of the three-phase power. In the exemplary embodiment, the ac bus26 electrically communicates with downstream power conversion anddistribution circuitry 29 that provides power to various UPS protectedloads. For example, the exemplary downstream power conversion anddistribution circuitry 29 provides three-phase ac power to one UPSprotected load 14, while providing single-phase ac power to another UPSprotected load 14. As will be appreciated by those of ordinary skill inthe art in view of the following discussion, the exemplary PDS 10 mayinclude any number of protected loads 14 operating at any number ofpower levels.

The exemplary ac bus 26 includes switching/distribution/protection (SDP)circuitry 16 to manage the transmission of operating power to theprotected loads 14. For example, the ac bus 26 includes fuses 30 thatmitigate the likelihood of improper power levels affecting the variouscomponents of the PDS 10. However, these fuses 30 are merely one exampleof protection circuitry and devices, which include circuit breakers andinterruption devices, to name but a few devices. The exemplary ac bus 26also includes static transfer switches 32, which are under the directionof the main processor/controller 24, for example. The exemplary statictransfer switches 32 control from which power source (e.g., the externalpower source 12, the UPS power source 20 and/or the auxiliary powersource 18) the protected loads 14 receive operating power. Of course,the static transfer switches 32 are merely one example of a switchingcircuit or device, and those of ordinary skill in the art may envisageany number of devices in view of the present discussion.

As discussed above, to mitigate the effects of a loss of the externalpower source 12, the PDS 10 includes an auxiliary power source 18. Inexemplary embodiment, the auxiliary power source 18 includes a dieselgenerator 34 that is coupled to a motor starter 36. Thus, in the eventexternal power is lost, the main processor/controller 24 instructs themotor starter 36 to activate the diesel generator, for instance. In theexemplary PDS 10, power filtration circuitry 38 located electricallybetween the diesel generator 34 and the ac bus 26 conditions the powergenerated by the diesel generator 34 to an appropriate level for the acbus 26. Unfortunately, the exemplary diesel generator 34 does notinstantaneously reach an operational state, i.e., a state at which thegenerator 34 is capable of providing operating power.

Accordingly, the exemplary PDS 10, as discussed above, includes the UPSpower source 20. The exemplary UPS power source 20, via the ac bus 26,provides transient operating power to the UPS protected loads 14 and, assuch, bridges the interval between the loss of external power and theactivation of the diesel generator 34.

During conventional operations (i.e., operating under external power),the UPS power source 20 receives external operating power via the ac bus26. In the exemplary UPS power source 20, first power conversioncircuitry 40, which is bi-directional, receives ac power from the ac bus26 and converts this ac power into dc power. By way of example, theexemplary first power conversion circuitry 40 rectifies 480 Vac powerinto 800 V dc power. As will be appreciated by those of ordinary skillin the art, the exemplary first power conversion circuitry 40 includesan assembly of inverters and rectifiers that appropriately condition theinput power to a desired output level. Indeed, any number of input powerlevels can be converted into any number of output levels, in accordancewith the appropriate design parameters of a given system.

In the exemplary embodiment, this dc power is then distributed tovarious components of the PDS 10 over a dc bus 42. As one example, thedc bus 42 is in electrical communication with the battery power source22. Accordingly, during conventional operations, the dc bus 42 feeds dcpower to exemplary charging circuitry 44 that, in turn, charges abattery bank 46. By way of example, the exemplary battery power source22 includes rechargeable nickel-cadmium batteries; of course, othertypes of batteries may be envisaged.

The dc bus 42 also feeds into and communicates with second powerconversion circuitry 48 of the UPS power source 20. Like the first powerconversion circuitry 40, the exemplary second power conversion circuitry48 includes appropriately arranged rectifiers and inverters and isbi-directional. This exemplary second power conversion circuitry 48,during conventional operating conditions, is configured to receive dcpower from the dc bus 42 and output three-phase ac power at a variablefrequency. To select the frequency of the output ac power, the exemplaryUPS power source 20 includes frequency control circuitry 50, which is incommunication with the main processor/controller 24.

The ac power output from the second power conversion circuitry 48provides operating power to an induction device 52 that operates as aninduction motor during conventional operating conditions. That is, theexemplary second power conversion circuitry 48 provides power to thestator windings of the exemplary induction device 52 to cause rotationof the rotor of the induction device. (See FIG. 4.)

In the exemplary UPS power source 20, the induction device 52 ismechanically coupled to a kinetic energy storage device, such as theillustrated flywheel 54. Accordingly, during conventional operations,induction device 52 acts as an induction motor and energizes theflywheel 54. That is, the rotation of the rotor (See FIG. 4) of theinduction device causes the flywheel 54 to rotate as well. To monitorthe operation of the induction device 52 or the flywheel 52, theexemplary UPS power source includes sensing devices, such as theillustrated speed sensor 56. The exemplary speed sensor 56 is configuredto determine a rotational rate (i.e., rotations per minute) of the rotoror the flywheel, for example. Advantageously, the exemplary speed sensor56 is in communication with the main processor/controller 24.Advantageously, the induction device when operating as an inductionmotor may be harnessed to operate a given piece of machinery, such as apump element, for example.

FIG. 3 illustrates an exemplary induction device 52 and flywheelassembly 54. The exemplary assembly includes a base 60 onto which theinduction device 52 and flywheel 54 are mounted. To increase thestructural integrity of the assembly, the base 60 includes a series ofstruts 62 disposed between legs 64 of the base 60. To support theinduction device 52 and the flywheel 54, the exemplary assembly includestrapezoidal shaped mounting structures 66 that secure these componentsto the base 60.

The exemplary induction device 52, as discussed further below, is aninduction generator/motor. To facilitate electrical communications toand from the exemplary induction device 52, a conduit box 68 isincluded. By way of example, the conduit box 68 includes connections tocouple the exemplary induction device 52 to the ac power bus 26 and, assuch, facilitates the receipt of operating power and the transmission ofgenerated power, for instance. Advantageously, the exemplary inductiondevice 52 includes a cooling system 70 that draws air into the inductiondevice 52 and expels the air from a vent 72 located at the opposite endof the device 52. Indeed, in the exemplary induction device 52, thecooling system 70 draws in air and generates airflow through the device52, as represented by directional arrows 73. (See FIG. 4.)

The exemplary induction device 52 is mechanically coupled to theflywheel 52 via a shaft assembly 74. Although the present embodimentillustrates a single flywheel, embodiments with two or more flywheelsare envisaged. Indeed, the induction device 52 may be coupled to a pairof flywheels that are disposed on opposite ends of the induction device52. Furthermore, it is envisaged that the rotor, via the shaft assembly74, can be coupled to a gearbox, for example, that distributes thetorque of the rotor to any number of flywheels 54. Advantageously, theuse of multiple flywheels facilities the use of smaller flywheels inmaintaining a desired amount of stored kinetic energy within the system.

The shaft assembly 74 mechanically correlates the rotation of the rotor(see FIG. 4) of the induction device 52 with the rotation of theflywheel 54. That is to say, the rotational rate (e.g., rpm) of therotor corresponds with the rotational rate of the flywheel 54, forexample. However, the induction device 52 and the flywheel may bemechanically coupled via other mechanical assemblies, such as gears andspeed reducers, that impact the rotations rates of the rotor and theflywheel with respect to one another. Additionally, as discussed furtherbelow, the exemplary flywheel 54 includes bearing assemblies 76 that arecoupled the mounting structures 66 and that facilitate rotationalmovement of the flywheel 54.

FIG. 4 provides a partial cross-section view of the induction device 52and flywheel 54 along line 4—4. To simplify the discussion, only the topportions of the induction device 52 and flywheel 54 are shown, becausethe structures of these components are essentially mirrored along theirrespective centerlines.

Beginning with the exemplary induction device 52, it includes a frame 90and drive-end and opposite drive-end endcaps 92 and 94 respectively.These endcaps 92 and 94, in cooperation with the frame 90, provide anenclosure or device housing for the exemplary induction device 52.Within the enclosure or device housing resides a plurality of statorlaminations 96 juxtaposed and aligned with respect to one another toform a stator core 98. The stator laminations 96 each include featuresthat cooperate with one another to form slots that extend the length ofthe stator core 98 and that are configured to receive one or more turnsof a coil winding 100, illustrated as coil ends in FIG. 4. These coilwindings 100 are in electrical communication with the ac bus 26 (seeFIG. 3). Accordingly, the coil windings 100 receive operating power fromthe ac bus 26 and provided generated power to the ac bus 26, asdiscussed further below. Each stator lamination 96 also has a centralaperture. When aligned with respect to one another, the centralapertures of the stator laminations 96 cooperate to form a contiguousrotor passageway 102 that extends through the stator core 98.

In the exemplary induction device 52, a rotor 104 resides within thisrotor passageway 102. Similar to the stator core 98, the rotor 104 has aplurality of rotor laminations 106 aligned and adjacently placed withrespect to one another. Thus, the rotor laminations 106 cooperate toform a contiguous rotor 108. The exemplary rotor 104 also includes rotorend rings 110, disposed on each end of the rotor 104, that cooperate tosecure the rotor laminations 106 with respect to one another. Theexemplary rotor 104 also includes rotor conductor bars 112 that extendthe length of the rotor 104. In the exemplary induction device 52, theend rings 110 electrically couple the conductor bars 112 to one another.Accordingly, the conductor bars 112 and the end rings 110 comprisenonmagnetic, yet electrically conductive materials and form one or moreclosed electrical pathways. As discussed below, routing alternatingcurrent through the stator windings 100 induces current in the rotor104, specifically in the conductor bars 112, and causes the rotor 104 torotate. By harnessing the rotation of the rotor 104 via the shaftassembly 74, the flywheel 54 rotates as well. Conversely, rotating therotor 104 at a rate above the synchronous speed of the induction device,which is a function of the input ac power fed to the stator windings100, causes the induction device 52 to generate power, as discussedfurther below. Indeed, those of ordinary skill in the art willappreciate that the synchronous speed (N_(s); as measure in rotationsper minute) of an induction device is generally defined by the followequation:

${N_{s} = \frac{120(F)}{P}},$in which F represents the frequency of the input ac power in Hertz and Prepresents the even integer number of poles of the induction device.

To support the rotor 104, the exemplary induction device 52 includesdrive-end and opposite drive-end bearing sets 120 and 122 that aresecured to the shaft assembly 74 and that facilitate rotation of therotor 104 within the rotor passageway 102. By way of example, theexemplary bearing sets 120 and 122 have a ball bearing construction;however, the bearing sets may have a sleeve bearing construction, amongother types of bearing constructions. Advantageously, the endcaps 92 and94 include features, such as the illustrated inner bearing caps 124,that releasably secure the bearing sets 120 and 122 within theirrespective endcaps 92 and 94. The exemplary bearing sets 120 and 122transfer the radial and thrust loads produced by the rotor 104 to thedevice housing. Each exemplary bearing set 120 and 122 includes an innerrace 130 disposed circumferentially about the shaft assembly 74. The fitbetween the inner races 130 and the shaft assembly 74 causes the innerraces 130 to rotate in conjunction with the shaft assembly 74. Eachexemplary bearing set 120 and 122 also includes an outer race 132 androlling elements 134 disposed between the inner race 130 and the outerrace 132. The rolling elements 134 facilitate rotation of the innerraces 130, while the outer races 132 remain stationary with respect tothe endcaps 92 and 94. Thus, the bearing sets 120 and 122 facilitaterotation of the shaft assembly 74 and the rotor 104 while providing asupport structure for the rotor 104 within the device housing, i.e., theframe 90 and the endcaps 92 and 94. To improve the performance of thebearing sets 120 and 122, a lubricant coats the rolling elements 134 andraces 130 and 132, providing a separating film between to bearingcomponents, thereby mitigating the likelihood of seizing, galling,welding, excessive friction, and/or excessive wear, to name a fewadverse effects.

The shaft assembly 74, in the exemplary embodiment, mechanically couplesthe rotor 104 to the flywheel 54. That is to say, the rotation of therotor 104 causes the flywheel 54 to rotate, and, conversely, rotation ofthe flywheel 54 causes the rotor 104 to rotate. The exemplary flywheel54 includes bearing sets 140, which each includes an inner race 142, anouter race 144, and a rolling elements 146 disposed therebetween.Similar to the bearing sets 120 and 122, the inner races 142 rotate inconjunction with the shaft assembly 74, while the outer races 144 remainstationary. Advantageously, the components of the exemplary bearing sets140 are coated with a lubricant, to mitigate the likelihood of seizing,galling, welding, excessive friction, and/or excessive wear, to name afew adverse effects.

Focusing on the exemplary flywheel 54, it is designed to store andtransfer kinetic energy. Accordingly, the exemplary flywheel 54 isformed of composite materials suited to maintain the inertial rotationof the flywheel. Of course, those of ordinary skill in the art in lightof the present discussion will appreciate that the flywheel 54 may beformed of any number of suitable structural materials. Furthermore, suchskilled artisans will also appreciate that the I-shaped cross-sectiondesign of the exemplary flywheel is merely but one example of a flywheeldesign.

With the foregoing figures (i.e., FIGS. 1–4) in mind, FIG. 5 illustratesan exemplary process for operation of the exemplary UPS power source 20within the exemplary power distribution system 10. As discussed above,during conventional operating conditions, the ac power bus 26 providesac power from the external power source 12 to the stator windings 100 ofthe induction device 52. More specifically, in the exemplary inductiondevice 52, the ac bus 26 provides ac power to the first power conversioncircuitry 40, which coverts the inputted ac power to a dc power. Via thedc bus 42, this dc power is provided to second power conversioncircuitry 48, which converts the inputted dc power into an ac power at adesired frequency. This ac power is then provided to the stator windings100, inducing current in the conductor bars 112 and causing the rotor108 to rotate. Because the shaft assembly 74 mechanically couples therotor 104 to the flywheel 54, the flywheel 54 rotates at the rotationalrate (i.e., rpm) of the rotor 104. Thus, the electrical energy from theexternal power source 12 is converted into kinetic energy and stored inthe flywheel 54. That is to say, the flywheel 54 is energized, asrepresented by Block 150. If the external power source is providingpower to the PDS 10, the then UPS power source 20 remains in theenergizing state, as represented by Block 152.

However, if a loss of external power is detected, by the mainprocessor/controller 24, for instance, then the UPS power source 20switches to a fault status state, as represented by Block 152. In theevent of a fault status state (i.e., a loss of external power), thestator windings 100 no longer receive ac power from the external powersource via ac power bus 26. However, the kinetic energy stored in therotating flywheel 54 continues to rotate the rotor 104, because therotor 104 is coupled to the flywheel. As discussed above, the exemplaryspeed sensor 56 monitors and detects the rotational rate of the flywheel54 in rotations per minute (rpm), for instance, as represented by block154. (As will be appreciated by those of ordinary skill in the art inview of the present discussion, the exemplary flywheel 54 and theexemplary rotor 104 rotate at the same rate, which is measured in rpm.)

Immediately upon the loss of external power, the frequency controlcircuitry 50, in response to inputs from the speed sensor 56 and/or themain processor/controller 24, directs the exemplary second powerconversion circuitry 48 to adjust the output frequency thereof, togenerate power from the induction device 52. That is, the frequencycontroller 50 directs the second power conversion circuitry 48 to outputac power at a frequency such that the rotor 104 is rotating faster thanthe synchronous speed of the induction device 52. Again, the synchronousspeed of the induction device 52 is partially defined by the frequencyof the ac power provided to the stator windings 100. Thus, by selectinga frequency that defines a synchronous speed for the induction device 52that is less than the rotation rate of the flywheel, the inductiondevice 52 acts as an induction generator and, as such, provides agenerated ac power to the second power conversion circuitry 48. As theflywheel 54 loses kinetic energy and slows down, the speed sensor 56monitors this reduction in speed and calculates an ac frequency thatmaintains operation of the induction device 52 as an inductiongenerator. Blocks 156 and 158 represent these steps of the exemplaryprocess.

In the exemplary process, the second power conversion circuitry 48receives the generated ac power and converts this power to dc power fortransmission over the dc bus 42. The first power conversion circuitry 40then receives the dc power from the dc bus 42 and converts the input dcpower into an ac power appropriate for the ac bus 26, which distributesthe power to downstream locations, such as the UPS protected loads 14.

The exemplary process also includes activating the auxiliary powersource 18, such as the exemplary diesel generator 34. By way of example,the exemplary diesel generator 24 is activated via a motor starter,which takes a few seconds to bring the diesel generator online, forinstance. Accordingly, the UPS power source 20 provides a bridge betweenthe time at which external power is lost and the time that the auxiliarypower is brought on-line. Once the auxiliary power source is broughton-line, the PDS 10 obtains its operating power from the auxiliary powersource, as represented by Blocks 160 and 162.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1. A method for providing transient power to a load, comprising:energizing a kinetic energy storage device that is mechanically coupledto a rotor of an electric machine; actuating the rotor via the kineticenergy storage device; providing alternating current (ac) power at aselected frequency to stator windings disposed in a stator of theelectric machine to generate power from the electric machine; andconditioning the generated power to match the frequency and voltage ofan external alternating current power configured to provide operatingpower to a load during operation.
 2. The method as recited in claim 1,comprising sensing a parameter of the kinetic energy storage device orthe rotor and basing the selected frequency on the parameter.
 3. Themethod as recited in claim 2, comprising determining the rotational rateof the rotor.
 4. The method as recited in claim 2, comprising rectifyinggenerated power from ac power to direct current (dc) power.
 5. Themethod as recited in claim 4, comprising inverting dc power to ac power.6. A method for providing transient power to a load, comprising:energizing a rotatable flywheel that is coupled to a rotor of anelectric machine; monitoring an external power source that providesoperating power to the load; providing first alternating current (ac)power at a variable frequency to stator windings disposed in a stator ofthe electric machine to generate second ac power via the electricmachine upon loss of the external power; and conditioning the second acpower to provide transient operating power to the load.
 7. The method asrecited in claim 6, comprising sensing an operating parameter of therotor or the rotatable flywheel and basing the variable frequency on theparameter.
 8. The method as recited in claim 6, comprising energizingthe rotatable flywheel by inducing a current in electrical conductorsextending through the rotor.
 9. A system for providing a transient powersupply, comprising: means for energizing a kinetic energy storage devicethat is mechanically coupled to a rotor of an electric machine; meansfor actuating the rotor via the kinetic energy storage device; means fordetermining an operating parameter of the kinetic energy device or therotor; means for providing alternating current (ac) power at a selectedfrequency to stator windings disposed in a stator of the electricmachine to generate power, wherein the selected frequency is based onthe operating parameter; and means for conditioning the generated powerto match the frequency and voltage of an external alternating currentpower configured to provide operating power to a load during operation.